Machines, such as wheel loaders and haul trucks, generally include a drivetrain that provides power to traction devices of the machines. The drivetrain is made up of at least three different elements, including a power source (e.g., an engine), a transmission driven by the power source, and a differential that divides power from the transmission between paired traction devices. The differential allows the paired traction devices to be driven at different speeds to accommodate turning of the machine.
A differential generally consists of a main pinion gear that is driven by the transmission to rotate a crown gear. A carrier housing is fixed to rotate with the crown gear, and includes two or more (e.g., four) different spider pinions internally located around a circumference of the carrier housing. The spider pinions are oriented radially inward and rotatably disposed on a spider shaft (e.g., a cross having four shaft ends), whose ends are connected to the carrier housing. Thus, when the carrier housing rotates about its own axis, the spider pinions also rotate about the same axis. In addition, each spider pinion spins about its own axis, which is oriented generally orthogonal to and passes through the axis of the carrier housing. A side gear is mounted at each end of the carrier housing and intermeshes with the spider pinions. The side gears are rotatable about the axis of the carrier housing, and connected to half-shafts that extend outward from the differential to respective ones of the paired traction devices. With this configuration, an input rotation provided via the main pinion gear results in separate rotations of the traction devices with substantially equal torque. During straight travel of the machine over good ground conditions, both traction devices are driven at the same speed. During turning or poor ground conditions, one traction device (e.g., the outside traction device during a turn or the slipping traction device) speeds up as the remaining traction device slows down.
While acceptable for some applications, the conventional differential can be problematic in other applications. In particular, because of the configuration of typical spider pinions, a moment is created when teeth of the spider pinions engage corresponding teeth of the side gears. This moment causes the spider pinions to tilt about the spider shaft ends. This tilting can restrict lubrication flow along the spider shaft (i.e., inside bores of the spider pinions), and even cause mechanical engagement between bore walls of the spider pinions and the spider shaft in some situations. The restricted lubrication and mechanical engagement causes premature wear of the differential.
One attempt to extend a useful life of a differential is disclosed in US Patent Publication No. 2010/0151983 (the '983 publication) of Ziech et al. that published on Jun. 17, 2010. Specifically, the '983 publication discloses a differential having a case, with a ring gear connected to an outer surface of the case and intermeshed with a pinion gear. Four recesses are formed within an inner surface of the case and directed radially inward into a hollow cavity in the case. The recesses are equally spaced around a circumference of the case. A wear cup is located within each of the recesses, and a tab of the wear cup is received within a slot in the case to prevent rotation of the wear cup. The wear cup has a flat base, and side walls that are perpendicular to the base. A side pinion is located within each of the wear cups. Each pinion has a flat heel end that fits inside the corresponding wear cup, a toe end, and a cylindrical wall that extends from the heel end to the toe end. The heel end directly contacts the flat base of the cup, and the side walls of the cup engage the cylindrical wall of the pinion to drive rotation of the pinion about an axis of the case. Side gears are also located within the case and mesh with the side pinions. The side gears are hollow and include splines that mesh with corresponding splines of half-shafts that protrude from the case. This design eliminates the need for a spider shaft.
Although the differential of the '983 publication may not suffer from mechanical engagement between the side pinions and a spider shaft (because the differential of the '983 publication does not include a spider shaft), the differential may still be less than optimal. In particular, the moment discussed above that can be created by engagement of the side pinions with the side gears may still exist. This moment may cause the heel end of the side pinions to tilt within the cups, making mechanical engagement between the cylinder wall of the side pinions and the cup side walls possible. In the same manner described above, this engagement may restrict lubrication of the toe end of the pinion gear and result in premature wear.
The disclosed differential is directed to overcoming one or more of the problems set forth above and/or other problems of the prior art.